Authigenic chlorite occurrence,enrichment factor and its impacts on reservoir petrophysics in Member 4 of Shahejie Formation in A21 structure,Liao Zhong sag

In the case of Well A21-2 in A21 sructure,Liao Zhong sag,authigenic chlorite occurrence,enrichment factor and its impacts on reservoir petrophysics are analyzed in Member 4 of Shahejie Formation.The results have shown that there are two stages of authigenic chlorite in the Member 4 reservoir,i.e.earlier grain-coating or pore-lining chlorite and later pore-filling chlorite,with the later one higher in content.Several factors,such as early hydrolysis of mafic minerals in volcanic detritus,delta front environment in a brackish lake and a closed and over-pressured diagenesis system,are the keys of authigenic chlorite enrichment in the Member 4 reservoir.The earlier grain-coating chlorite has inhibited some quartz overgrowth,but SiO2 can still precipitated as a lot of microcrystalline quartz because the Member 4 reservoir is a closed and over-pressured system,making the correlation between porosity and chlorite content in the reservoir be not obvious.The later pore-filling chlorite has relatively well developed,which increase specific surface area of pores and make the pore throats be complicated and more tiny,causing great damage to permeability of the Member 4 reservoir.As a result,there is a weak negative correlation between permeability and the content of authigenic chlorite in this reservoir.In addition,the strong acid sensitivity of the reservoir may be closely related with the high content of authigenic chlorite,and it is suggested that the iron chelating agent and deoxidant should be added when acidizing the reservoir,in order to reduce the harm of strong acid sensitivity to hydrocarbon zones.